The present invention relates to a numerically controlled grinding machine, and more particularly to a feed control apparatus for a grinding machine which includes a wheel head with a grinding wheel of the angular type mounted thereon.
In such a conventional grinding machine as described above, a work table is slidably mounted on a bed in a first axis direction for supporting thereon a workpiece and rotating it about the first axis, a wheel head is slidably mounted on the bed in a second axis direction perpendicular to the first axis, and a grinding wheel is rotatably mounted on the wheel head and is formed at the outer periphery thereof with first and second grinding surfaces, the first grinding surface being arranged in parallel with the first axis for grinding a cylindrical portion of the workpiece, and the second grinding surface being arranged in parallel with the second axis for grinding a shoulder portion of the workpiece adjacent to the cylindrical portion. The conventional grinding machine further comprises first and second feed mechanisms for moving the work table and the wheel head respectively in the first and second axis directions, and a numerical feed control apparatus for activating both the feed mechanisms on a basis of numerical control data and for effecting relative movement between the work table and the wheel head to move the grinding wheel along a path extending across the second axis at an acute angle. In the numerical control data for the feed control apparatus, it is necessary to store each movement amount of the work table in the first axis direction in relation to each movement amount of the wheel head in the second axis direction. In the case that the moving direction of the grinding wheel is determined at an acute angle .theta. with respect to the second axis direction and that movement amount of the wheel head is determined as a value r, each calculation of r tan .theta. is required to determine each movement amount .DELTA.Z of the work table. For this reasons, the input work for the numerical control data becomes troublesome. In general, the value of r tan .theta. includes a fraction, causing an error in determination of the movement amount of the work table.